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Sex Linkage and Recombination by CHED on June 17, 2017 lesson duration of 10 minutes under General Biology 2 generated on June 17, 2017 at 02:30 pm Tags: Sex Linkage and Recombination CHED.GOV.PH K-12 Teacher's Resource Community Generated: Jun 17,2017 10:30 PM Sex Linkage and Recombination ( 1 hour and 10 mins ) Written By: CHED on July 17, 2016 Subjects: General Biology 2 Tags: Sex Linkage and Recombination Resources n/a n/a Content Standard 1. Mendel’s Laws of Inheritance 2. Sex Linkage 3. Central Dogma of Molecular Biology 4. Recombinant DNA Performance Standard 1. make a pedigree analysis in the learner’s family using a simple genetic trait 2. make a research paper/case study/poster on genetic diseases 3. make a diagram (e.g., pictogram, poster) showing the evolution of a domesticated crop 4. differentiate the 3-Domain Scheme from the 5-Kingdom Scheme of classification of living things Learning Competencies Explain sex linkage and recombination Introduction 5 mins Communicating Learning Objectives 1. Cite the learning objectives, which are as follows: I. illustrate the transmission of an X-linked and a Y-linked character 1/5 CHED.GOV.PH K-12 Teacher's Resource Community II. compute the probability of the occurrence of a sex-linked trait III. give examples of other sex-related traits Relevant Vocabulary 2. State the relevant vocabulary: I. Sex linked trait. The gene (pair) that determines a character (e.g. hemophilia) is located on the sex chromosomes II. X-linked trait. A sex-linked trait is where the gene or allele for the trait is found on the X chromosome III.Color Colorblindness. blindness.An AnX-linked X-linkedrecessive recessivetrait traitwhere whereaaaffected affectedindividual individualcould couldnot notdistinguish distinguishred redfrom fromgreen greencolor color III. (red green color blindness) Hemophilia. X-linked recessive where affected individual suffers from delayed blood clotting during IV.IV. Hemophilia. AnAn X-linked recessive traittrait where an an affected individual suffers from delayed blood clotting during injuries because of the absence of certain blood clotting factors V. Y-linked trait. A sex-linked trait where the gene or allele for the trait is found on the Y chromosome VI. Hypertrichosis pinnae auris. A Y-linked trait where affected males have hair growing from their external ears VII. Other sex-related traits. A. Sex-influenced Sex-influenced traittrait- Any Any trait trait in in aa diploid diploid organism organism whose whose expression expression is is affected affected by by an an individual’s individual’s biological biological sex; sex; aa A. trait that occurs at a higher frequency in one sex over the other B. Sex-limited trait- Any trait in a diploid organism whose expression is limited to just one biological sex Teacher tip: Ask the learners to review the topic on recombination in Meiosis that they took up in BIO 1. Recombination or shufflingofofgenes/ genes/alleles allelesininMeiosis Meiosisresults resultstotovariation variationininthe thegenome genomeofofgametes, gametes,the thesperm spermcells cellsand andegg egg shuffling cells. In cell any of cell ofbody the body (somatic), are chromosome In humans, pair numbers are the In any the (somatic), therethere are chromosome pairs.pairs. In humans, pair numbers 1-22 1-22 are the autosomes or body chromosomes while the last (23rd) pair is the sex chromosome. Normal human human females females have have two two X X chromosomes chromosomes and and normal normal human human males males have have one one X X chromosome chromosome and and aa Y Y Normal chromosome; that is: XX- female XY- male Motivation 10 mins Case Study Present these three cases using pictures: 2/5 CHED.GOV.PH K-12 Teacher's Resource Community Use Use aa high high resolution resolution figure figure (photograph (photograph or or image image projected projected on on aa computer computer or or LCD) LCD) to to ensure ensure the the accuracy accuracy of of the the color color blindness Those could the figure normal; those cannot colorblind. In most cases, blindness test.test. Those that that could see see the figure are are normal; those that that cannot are are colorblind. In most cases, the the colorblindmales malesoutnumber outnumberthe thecolorblind colorblindfemales, females,which whichare arerare. rare.If Ifthere thereare areno nocolorblind colorblindindividuals individualsininthe theclass, class, colorblind the teacher will just have to mention as a matter of fact that colorblind females are rare. Be careful in conducting to discourage teasing of actual colorblind learners. Emphasize colorblind Be careful in conducting this this test test to discourage teasing of actual colorblind learners. Emphasize that that colorblind individuals are normal except that they could not distinguish between red and green colors. Misconception: Common Common misconception is that baldness occurs in males. Emphasize baldness does misconception is that baldness occurs onlyonly in males. Emphasize thatthat baldness does happen in women, although the frequency is much lower and is therefore rare. Instruction 25 mins Sex-linked traits Give the definition of an X-linked trait Explain why X-linked traits may occur more frequently in one sex over the other In humans, males and females are represented by different sex chromosomes Females have two X chromosomes in the nucleus of their cells. Males have one X chromosome and one Y chromosome in the nucleus of their cells. Depending on whether the trait is dominant or recessive, the expression pattern of the trait differs in males and females Colorblindness in humans as an example of sex-linked trait The alleles responsible for colorblindness is found on the X chromosome only The dominant allele is the normal allele; the recessive allele causes colorblindness Females need two copies of the recessive allele, one from each of the two X chromosomes, for the trait to be manifested. If they only have one copy of the recessive allele, they have normal color vision. However, they are carriers for the trait in that they may pass it on to their offspring. Males only need one recessive allele in their sole X chromosome for the trait to be expressed. Explain what happens to the expression patterns if the trait is X-linked and dominant. Use Table 2 as guide. Give the definition of a Y-linked trait Explain why there is difference in expression between males and females for Y-linked traits. (Since the allele is found only in the Y chromosome, and since only males have Y chromosomes, then only males will express the trait. Females CANNOT express Y-linked traits.) 3/5 CHED.GOV.PH K-12 Teacher's Resource Community Hypertrichosis pinnae auris as an example of a Y-linked trait If a male has the allele responsible for the trait, then his Y chromosome will possess that allele. Since he will pass on his Y chromosome to his sons, then all his sons will inherit the trait, and they, in turn, can pass on the allele to their sons. 3. Describe other sex-related traits Sex-influenced trait Give the definition Explain why traits may be expressed differently between sexes Hormonal or physiological differences between the sexes cause differences of expression of certain genes Baldness in humans as an example of a sex-influenced trait. See Table 1 how baldness is hypothesized to be expressed by a single pair of alleles, with B as the dominant allele for baldness and b as the recessive normal allele. Sex-limited traits Give the definition Explain why traits may be limited to one sex only Hormonal or physiological differences between sexes may limit the expression of some genes to one biological sex only Functional mammary glands as an example of a sexlimited trait. Only females can express functional mammary glands that produce milk immediately after giving birth. Note that baldness behaves like a dominant trait in males in that only one dominant allele is needed for baldness to be expressed. On the other hand, the trait behaves like a recessive trait in women in that they need both dominant alleles to be present for baldness to be expressed. Practice 20 mins 1. Divide learners into groups of four. 2. Ask each group to answer a set of questions related to sex-related traits in humans. See sample questions. Enrichment 10 mins As a homework, provide this narrative to the class: The last Emperor of Russia, Nicolas II, was married to Empress Alexandra, and they had five children, Olga, Tatiana, Maria, Anastasia, and Alexis. Alexis was the only one who was afflicted with hemophilia or the royal bleeding disease; all other members were normal Research on this medical condition and determine the mode of inheritance. If only Prince Alexis was afflicted with the disease, determine his genotype. What could be the genotypes of the Emperor and Empress? Is it possible that each daughter could have been a carrier? Teacher tip: Hemophilia is an X-linked recessive trait. Empress Alexandra was most likely a carrier of the trait (XCX). She 4/5 CHED.GOV.PH K-12 Teacher's Resource Community was a descendant of Queen Victoria of the United Kingdom, who herself was a probable carrier. The Emperor was completely unaffected and therefore had an XY genotype. Based on the genotypes of the parents, Alexis had an XCY genotype, with the defective X chromosome carrying the allele for hemophilia coming from his mother. Each daughter, in turn, had a 50% probability of being a carrier, but they could NEVER have been affected Download Teaching Guide Book 0 mins 5/5 Powered Poweredby byTCPDF TCPDF(www.tcpdf.org) (www.tcpdf.org)